It is well known to subject steels to thermo-chemical treatments to create a hardened surface layer or case. Such treatments can involve several heating cycles to achieve the desired properties and post-machining is often necessary to compensate for dimensional changes and unwanted surface features. It is also known to subject steel to ion nitriding but in the case of conventionally nitrided bearing components additional steps are needed after nitriding to remove the friable compound layer which forms on the surface.